1) Field of the Invention
The present invention relates to a process for making a lower molecular weight polymer from a solid stated higher molecular weight feed stock chip. In particular, the present invention relates to a process, wherein the molecular weight of an industrial resin or a bottle resin is reduced in a controlled manner by the introduction of ethylene glycol. More specifically, the ethylene glycol may be introduced in an extruder. If the industrial resin is to be employed for industrial fibers, the ethylene glycol may be added at the extruder for spinning the industrial fiber. On the other hand, should the high molecular weigh chip be used for bottle resin, the molecular weight may be reduced by the introduction of ethylene glycol at the extruder for injection molding of preforms of a lower molecular weight. The ethylene glycol/polymer ratio is determined by the reduction in molecular weight that is required. The preferred resin is polyester polymer or copolymer, and especially polyethylene terephthalate (PET).
2) Prior Art
Polyester chip is generally employed to make containers, such as soft drink bottles; film for multiple uses including food wrap, for example; molded parts for appliances or the automotive industry, for example; and fiber for the textile or industrial uses. Of the many uses for polyester chip, containers and industrial fibers require a high molecular weight chip. Primarily the high molecular weight is obtained by running polyester chip through a solid state polymerizer to increase its molecular weight.
In the fiber making art, low molecular weight chip may be used to make textile products. Textile products do not require the high tensile strength and increased physical properties required for industrial fiber uses. Typical industrial fiber uses include seat belts, airbags, tire cord, and other reinforcement for conveyor belts, hoses, and v-belts, for example.
The normal process used for high molecular weight chip is to solid state polymerize chips from the melt phase polymerization process of a lower molecular weight. Often, a production line that is capable of producing high molecular weight chip can also be reconfigured to make a lower molecular weight chip. However, it is necessary to interrupt production to either decouple the solid-state polymerization, or change the solid state polymerization process conditions in order to make the lower molecular weight chip. Switching the process in a production line from a high molecular weight chip to a lower molecular weight chip and vice-versa is not only timely but also costly. Therefore it would be desirable to develop a process in which the line does not have to be stopped and reconfigured in order to make lower molecular weight chip. In particular, it would be especially desirable to produce the high molecular weight chip under constant conditions and to lower its molecular weight in a controlled and accurate fashion without modifying the production line to produce the required molecular weight of the product that is being manufactured.
In recycling efforts for polyester, it is known that polyester can be recycled by employing either a glycolysis process or a hydrolysis process. The hydrolysis process uses water or steam to break down the polyester into its monomers for recycle purposes. No further discussion of this process is necessary with respect to the present invention.
In a glycolysis recycle process, the polyester to be recycled is heated and subjected to a high temperature glycol stream which reverses the reaction of producing polyester and therefore produces monomers (the starting materials for making polyester) such that the monomers can then be reused to make polyester. Consequently, the addition of glycol to polyester, thereby producing a glycolysis reaction, is known in the industry.
It is also known in the industry to add glycol to polyester as a carrier for master batch operations. Master batch operations are generally employed when it is desirable to uniformly mix a small amount of an additive into a large amount of polymer, such as polyester. In order to obtain the necessary uniformity, a master batch containing, for example, 10% of an additive with the remainder being glycol, may be added to polyester to produce a final polyester composition having a half percent additive. In order to achieve good dispersion of the additive in the master batch, glycol is added during compounding the master batch. The molecular weight of the master batch is chosen to match the additive free polymer to achieve the desired molecular weight.
It is also known in the textile industry to add glycol to polyester resin to prevent pilling. Pilling occurs in a garment that contains synthetic fiber, such as polyester fiber. When a filament or two of polyester in the textile garment breaks, it tends to roll into a very small ball and produce an esthetically unpleasing garment. To avoid pilling, glycol is added to the polyester resin at spinning which results in a reduced or lower strength physical property fiber (yet this fiber still has physical properties superior to cotton, for example).
In summary, in prior art processes there are 3 situations where glycol is added to polyester, namely: 1) the recycle of polyester; 2) masterbatch operations, and 3) to reduce pilling in textile garments. In each of these situations the final molecular weight, expressed in terms of intrinsic viscosity (IV), of the polyester chip or polyester resin is below 0.7 and in most cases is between 0.4 and 0.6 IV. Polyester chips or resin having such a low IV would not be suitable for industrial applications requiring high molecular weight for good physical properties.
U.S. Pat. No. 5,308,892 to Zickler et al. discloses a polyester masterbatch which was produced with 0.01 to 5 moles of a diol (ethylene glycol) per mole of polyester. The initial IV of the polyester used for the master batch was at least 0.5 dl/g and it is reduced further by the addition of the ethylene glycol in the master batch process.
U.S. Pat. No. 4,359,557 to Watkins et al. discloses a process for manufacturing polyethylene terephthalate fibers having improved low pilling properties by add/mixing ethylene glycol with the polyethylene terephthalate in an extruder. The original polymer material has an IV of about 0.56 to about 0.60 with about 0.25% by weight ethylene glycol blended therewith. The resultant molecular weight is about 0.39 to about 0.43. Based on the weight of the polyester, this means that 2500 ppm of ethylene glycol was added to reduce the inherent molecular weight in claim 1, for example, from 0.56 to 0.40.
Japanese patent publication 49-1256 to Iwaki et al. discloses a method for making a low molecular weight polyester fiber having an improved pilling by mixing with the polyester ethylene glycol or propylene glycol. In each example, however, magnesium stearate was added as a necessary component to lower the molecular weight.
In the broadest sense, the present invention comprises a process for reducing the molecular weight of a solid stated polyester feed stock resin comprising obtaining polyester resin having an IV greater than about 0.8 dl/g; and mixing ethylene glycol with said polyester wherein said ethylene glycol is present in a stoichiometric amount to reduce the IV to the required level.
Furthermore, in the broadest sense of the present invention, said resin has color properties about the same as the polyester resin without the introduction of the ethylene glycol component.
In the broadest sense the present invention also comprises a method of reducing the IV of a solid stated polyester resin feed stock suitable for spinning comprising obtaining a polyester resin having an IV greater than about 0.8, introducing said polyester resin into an extruder for extruding/spinning resin into fiber, introducing ethylene glycol into said, extruder, and extruding/spinning said polyester resin to produce fibers having an IV lower than that obtained without the addition of ethylene glycol.
In the broadest sense the present invention also comprises a method of reducing the IV of a solid stated polyester resin feed stock suitable for injection molding comprising obtaining a polyester resin having an IV greater than about 0.8, introducing said polyester resin into an extruder for injection molding resin into an article (such as a preform for a plastic bottle), introducing ethylene glycol into said extruder, and extruding/injection molding said polyester resin to produce an article having an IV lower than that obtained without the addition of ethylene glycol.
In addition to the above, the present invention also has an IV standard deviation along the spin beam manifold in the range of less than about 0.01 in the process where the ethylene glycol and polyester are added at the throat of the extruder and mixed in the extruder prior to spinning into a fiber.